This application claims priority to Japanese Patent Application No. JP 2001-161918, filed on May 30, 2001, the disclosure of such application being herein incorporated by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a high frequency power amplifier using switching-driven transistors, and more particularly, to a high frequency power amplifier permitting continuously controlled power output and attaining improved amplification efficiency.
2. Description of the Related Art
High frequency power amplifiers are conventionally used as amplifiers for antenna output stages of communication devices, or the like. There are amplifiers having various characteristics and, among them, amplifiers having high efficiency as amplifiers are especially suitable for use in the transmitting sections of communication device terminals for digital mobile communication utilizing digital cellular phones or the like. Merits on low electric power consumption, namely extension of the utilization time for batteries of such portable devices, reduction of size of the battery, reduction of heat generation, or the like, are meaningful features for the portable devices.
As a high frequency power amplifier having the high efficiency thereof, a saturated type amplifier such as a field effect transistor (FET) operated in a saturated mode is well known. The saturated type amplifiers are separated in classes, in which a class B amplifier has efficiency higher than a class A amplifier, and a class C amplifier, having a theoretical efficiency of nearly 100%, has an efficiency even higher than the class B amplifier.
However, because the saturated type amplifier operates FET""s in their saturated states, it is impossible to control the outputs of the amplifier by changing the inputs thereof like a linear amplifier.
Accordingly, a method for changing output of the saturated type amplifier through a drain voltage of the FET is adopted. In such drain voltage control method, the output of the amplifier is controlled by a drain application voltage obtained by converting voltage according to an amount of control by a DC-DC converter. As a result, when adopting the drain voltage control method, the efficiency of the amplifier as a whole is directly affected by the efficiency of the DC-DC converter. In other words, the FET""s of the amplifier are operated in their saturated states or modes. That is, because the efficiency of the DC-DC converter is around 80% at the most, the efficiency of the whole of the amplifier is reduced to 80% owing to the efficiency of the DC-DC converter even if the FET""s are operated under the efficiency of nearly 100% on their saturated states.
The present invention has been conceived in consideration of the aforesaid problems in the prior art. It is preferable according to the invention to provide a high frequency power amplifier having further improved efficiency thereof in comparison with a conventional amplifier and having a structure such that its output can be controlled continuously by changes in the drain voltages of switching-driven transistors.
A first preferred embodiment of the present invention presents a high frequency power amplifier using a plurality of switching-driven transistors, the amplifier including a plurality of switching-driven transistors, the transistors being connected in parallel with each other; means or unit for applying a fixed drain voltage to part of the plurality of transistors; means or unit for applying a variable drain voltage to another part of the plurality of transistors according to a control value; means or unit for turning on or off an operation of the part of the plurality of transistors having fixed drain voltage applied thereon; and means or unit for controlling an output of the amplifier by turning variable an output of the amplifier through controlling a drain voltage of the other part of the plurality of transistors, as well as turning on the operation of the part of the plurality of transistors in a high output power region and, in a low output power region, turning off the operation of the part of the plurality of transistors that have been turned on.
According to the first preferred embodiment of the invention, the high frequency power amplifier is provided with the means or unit for controlling the output of the amplifier. The means controls the means for turning on or off the operation of the portion of the plurality of transistors, which are connected in parallel and are switch-driven, turning on the operation of the portion of the plurality of transistors in the high output power region and turning off the operation of the portion of the plurality of transistors in the low output power region. Consequently, the reduction of efficiency on the side of the other portion of the plurality of transistors, having variable drain voltage according to the control value, can be suppressed to a minimum. Thus, it becomes possible to control the output power of the amplifier while keeping relatively high efficiency.
A second preferred embodiment of the present invention further includes a matching circuit having a variable circuit constant, disposed on an output side of the plurality of transistors; and means or unit for optimizing the circuit constant of the matching circuit according to the output of the amplifier.
A third preferred embodiment of the present invention further has the means for optimizing the circuit constant including a means or unit for switching the circuit constant in accordance with the turning on or off of the operation of such portion of said plurality of transistors.
According to the second and the third preferred embodiments of the invention, as the amplifier being provided with the means for optimizing setting of the circuit constant of the matching circuit according to the output of the amplifier, it becomes possible to achieve the improvement of the stability thereof as well as the improvement of the efficiency thereof, in addition to the advantages of the first embodiment. Furthermore, the amplifier according to the third preferred embodiment switches the circuit constant in accordance with the turning on or off of the operation of the portion of the plurality of transistors, and thereby the operation of the amplifier can easily be implemented by means of a common controller.
A fourth preferred embodiment of the present invention presents the high frequency power amplifier according to the first preferred embodiment with the means for applying the variable drain voltage to the other part of said plurality of transistors including a means for enabling continuous control of the applied drain voltage.
A fifth preferred embodiment of the present invention has the high frequency power amplifier according to the fourth preferred embodiment including the means for enabling the continuous control of the drain voltage including a DC-DC converter.
According to the fourth and the fifth preferred embodiments of the invention, as the amplifier is provided with the means or unit (such as the DC-DC converter) for enabling the continuous control of the drain voltage to be applied to the transistors, it becomes possible to adjust the output power of the amplifier most suitably for preventing waste of electric power and for performing a more suitable operation thereof in addition to the advantages of the aforesaid first to the third preferred embodiments.